I am trying to clarify the contract for this method.
The documentation is:
/** Close the query execution and stop query evaluation as soon as
convenient.
* It is important to close query execution objects in order to
release
* resources such as working memory and to stop the query execution.
* Some storage subsystems require explicit ends of operations and
this
* operation will cause those to be called where necessary.
* No operations on the query execution or any associated
* result set are permitted after this call.
* This method should not be called in parallel with other methods
on the
* QueryExecution object.
*/
It is then unclear to me whether:
a) close MUST be called in all circumstances (i.e. it is part of the
contract of a QueryExcecution)
b) close SHOULD be called when you don't read all the results in a
result set or iterator
If (a) is the only correct code one where there is effectively a finally
block which calls close even in abnormal termination
Also can close() be called twice?
com.hp.hpl.jena.query.QueryExecution.execConstruct()
e.g.
QueryExecution exec =
QueryExecutionFactory.create(queryStr);
try {
return exec.execConstruct();
}
finally {
exec.close();
}
compared with
QueryExecution exec =
QueryExecutionFactory.create(queryStr)
return exec.execConstruct();
or:
return
QueryExecutionFactory.create(queryStr).execConstruct();
except in Exception-al circumstances execConstruct() runs the query to
completion, so any underlying ExtendedIterators run to termination and
do not need close being called, so maybe close() is redundant in this
case. But the contract for QueryExecution.close() is not the same as
that for ClosableIterator.close()
Of course the latter two suggest that somewhere in the implementation(s)
of execConstruct() there is a finally block to close the underlying
iterators ....
thanks
Jeremy
